1. Technical Field
The subject invention relates to a method for metallurgically bonding a cylinder liner with a cylinder block of an internal combustion engine.
2. Description of the Related Prior Art
It is becoming more and more common in today's automotive industry to form the cylinder block of internal combustion engines out of aluminum rather than cast iron. The aluminum is much lighter than the cast iron and contributes to a more fuel efficient automobile.
These aluminum engine blocks are typically provided with cylinder liners made of cast iron or other suitable material for providing a high wear resistent surface to the cylinder walls of the engine block. In order to prevent the liners from moving and rendering the engine inoperable, it is important that the cylinder liners be securely joined to the cylinder block.
One common method for joining the liner to the block is to create a mechanical interference between the liner and the block. One known method involves pressing the preformed liner into the engine block under an interference fit. Another method involves casting the cylinder block around the cylinder liners to form a mechanical interlock between the liners and the cylinder block. Although these types of liners have enjoyed some commercial success, they are deficient in that a mechanically joined liner tends to loosen over time. This is caused by the continuous thermal cycling of the engine and the different coefficients of expansion of the liner and cylinder block materials. The loosened liner tends to warp and lose its cylindrical shape as well as decrease the ability of the liner to transfer heat to the cylinder block. An example of such a liner is disclosed in U.S. Pat. No. 3,069,209 to Bauer, granted Dec. 18, 1962.
Another method for securing the liner to the cylinder block is to metallurgically bond the liner to the cylinder block. Such a method is disclosed in U.S. Pat. No. 1,710,136 to Angle et al, granted Apr. 23, 1929. Other examples include the U.S. Pat. Nos. 3,165,983, granted Jan. 19, 1965 and corresponding divisional U.S. Pat. No. 3,276,082, granted Oct. 4, 1966, both to Thomas, and U.S. Pat. No. 5,005,469, granted Apr. 9, 1991 to Ohta.
Although the method disclosed in the Thomas '983 and '082 patents reportedly form a metallurgical bond between the cylinder liner and the cylinder block, practice has shown that a satisfactory metallurgical bond is not formed. Although Thomas pays particular attention to the surface preparation of the liner prior to coating the liner with the bonding material, Thomas does not address the problems of bonding the molten cylinder block material with the resultant coating on the liner. In particular, the coating materials, such as zinc, develop an outer oxidized layer or skin after the liner has been coated. This is particularly true when the coating is applied by dipping the cylinder liners in a bath of molten zinc. As the coated liner is withdrawn from the molten bath of zinc and the coating is solidifying, the outer surface of the coating oxidizes. When the coated cylinder is subsequently disposed in the casting mold and molten cylinder block defining material is poured into the mold, the oxidized surface of the coating greatly inhibits the ability of the coating to alloy with the cylinder block material, thus preventing the formation of a satisfactory metallurgical bond upon cooling. Thomas does not address the problems associated with an oxidized coating as it relates to the success or failure of forming a satisfactory metallurgical bond.